[SPARK-22574][MESOS][SUBMIT] Check submission request parameters

## What changes were proposed in this pull request?

PR closed with all the comments -> apache#19793

It solves the problem when submitting a wrong CreateSubmissionRequest to Spark Dispatcher was causing a bad state of Dispatcher and making it inactive as a Mesos framework.

https://issues.apache.org/jira/browse/SPARK-22574

## How was this patch tested?

All spark test passed successfully.

It was tested sending a wrong request (without appArgs) before and after the change. The point is easy, check if the value is null before being accessed.

This was before the change, leaving the dispatcher inactive:

```
Exception in thread "Thread-22" java.lang.NullPointerException
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler.getDriverCommandValue(MesosClusterScheduler.scala:444)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler.buildDriverCommand(MesosClusterScheduler.scala:451)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler.org$apache$spark$scheduler$cluster$mesos$MesosClusterScheduler$$createTaskInfo(MesosClusterScheduler.scala:538)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler$$anonfun$scheduleTasks$1.apply(MesosClusterScheduler.scala:570)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler$$anonfun$scheduleTasks$1.apply(MesosClusterScheduler.scala:555)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler.scheduleTasks(MesosClusterScheduler.scala:555)
	at org.apache.spark.scheduler.cluster.mesos.MesosClusterScheduler.resourceOffers(MesosClusterScheduler.scala:621)
```

And after:

```
  "message" : "Malformed request: org.apache.spark.deploy.rest.SubmitRestProtocolException: Validation of message CreateSubmissionRequest failed!\n\torg.apache.spark.deploy.rest.SubmitRestProtocolMessage.validate(SubmitRestProtocolMessage.scala:70)\n\torg.apache.spark.deploy.rest.SubmitRequestServlet.doPost(RestSubmissionServer.scala:272)\n\tjavax.servlet.http.HttpServlet.service(HttpServlet.java:707)\n\tjavax.servlet.http.HttpServlet.service(HttpServlet.java:790)\n\torg.spark_project.jetty.servlet.ServletHolder.handle(ServletHolder.java:845)\n\torg.spark_project.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:583)\n\torg.spark_project.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1180)\n\torg.spark_project.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)\n\torg.spark_project.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112)\n\torg.spark_project.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)\n\torg.spark_project.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)\n\torg.spark_project.jetty.server.Server.handle(Server.java:524)\n\torg.spark_project.jetty.server.HttpChannel.handle(HttpChannel.java:319)\n\torg.spark_project.jetty.server.HttpConnection.onFillable(HttpConnection.java:253)\n\torg.spark_project.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)\n\torg.spark_project.jetty.io.FillInterest.fillable(FillInterest.java:95)\n\torg.spark_project.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93)\n\torg.spark_project.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303)\n\torg.spark_project.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148)\n\torg.spark_project.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136)\n\torg.spark_project.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671)\n\torg.spark_project.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589)\n\tjava.lang.Thread.run(Thread.java:745)"
```

Author: German Schiavon <germanschiavon@gmail.com>

Closes apache#19966 from Gschiavon/fix-submission-request.

(cherry picked from commit 0bdb4e5)
Signed-off-by: Marcelo Vanzin <vanzin@cloudera.com>

core/src/main/scala/org/apache/spark/deploy/rest/SubmitRestProtocolRequest.scala

@@ -46,6 +46,8 @@ private[rest] class CreateSubmissionRequest extends SubmitRestProtocolRequest {
     super.doValidate()
     assert(sparkProperties != null, "No Spark properties set!")
     assertFieldIsSet(appResource, "appResource")
+    assertFieldIsSet(appArgs, "appArgs")
+    assertFieldIsSet(environmentVariables, "environmentVariables")
     assertPropertyIsSet("spark.app.name")
     assertPropertyIsBoolean("spark.driver.supervise")
     assertPropertyIsNumeric("spark.driver.cores")

core/src/test/scala/org/apache/spark/deploy/rest/SubmitRestProtocolSuite.scala

@@ -86,6 +86,8 @@ class SubmitRestProtocolSuite extends SparkFunSuite {
     message.clientSparkVersion = "1.2.3"
     message.appResource = "honey-walnut-cherry.jar"
     message.mainClass = "org.apache.spark.examples.SparkPie"
+    message.appArgs = Array("two slices")
+    message.environmentVariables = Map("PATH" -> "/dev/null")
     val conf = new SparkConf(false)
     conf.set("spark.app.name", "SparkPie")
     message.sparkProperties = conf.getAll.toMap

resource-managers/mesos/src/main/scala/org/apache/spark/deploy/rest/mesos/MesosRestServer.scala

@@ -77,10 +77,17 @@ private[mesos] class MesosSubmitRequestServlet(
   private def buildDriverDescription(request: CreateSubmissionRequest): MesosDriverDescription = {
     // Required fields, including the main class because python is not yet supported
     val appResource = Option(request.appResource).getOrElse {
-      throw new SubmitRestMissingFieldException("Application jar is missing.")
+      throw new SubmitRestMissingFieldException("Application jar 'appResource' is missing.")
     }
     val mainClass = Option(request.mainClass).getOrElse {
-      throw new SubmitRestMissingFieldException("Main class is missing.")
+      throw new SubmitRestMissingFieldException("Main class 'mainClass' is missing.")
+    }
+    val appArgs = Option(request.appArgs).getOrElse {
+      throw new SubmitRestMissingFieldException("Application arguments 'appArgs' are missing.")
+    }
+    val environmentVariables = Option(request.environmentVariables).getOrElse {
+      throw new SubmitRestMissingFieldException("Environment variables 'environmentVariables' " +
+        "are missing.")
     }
 
     // Optional fields
@@ -91,8 +98,6 @@ private[mesos] class MesosSubmitRequestServlet(
     val superviseDriver = sparkProperties.get("spark.driver.supervise")
     val driverMemory = sparkProperties.get("spark.driver.memory")
     val driverCores = sparkProperties.get("spark.driver.cores")
-    val appArgs = request.appArgs
-    val environmentVariables = request.environmentVariables
     val name = request.sparkProperties.getOrElse("spark.app.name", mainClass)
 
     // Construct driver description